1. Field of Invention
The present invention relates to driving devices for driving liquid-crystal panels for use with a TFD (Thin Film Diode) driving method, a TFT (Thin Film Transistor) driving method, and a simple-matrix driving method, and to a liquidcrystal device comprising a liquid-crystal panel and a driving device. More particularly, the present invention relates to an device for driving a transflective liquid-crystal panel which comprises a polarizer, a transflector, and a light source. The device being capable of serving dual purposes of a reflective-type such that a display is produced by reflecting external light, and of a transmissive-type such that a display is produced by transmitting light-source light.
2.Description of Related Art
In a conventional transmissive-type liquid-crystal panel using TN (Twisted Nematic) liquid-crystal, STN (Super-Twisted Nematic) liquid-crystal, and the like, generally, relatively satisfactory brightness is obtained by light-source light. On the other hand, in order that the contrast ratio to be sufficient, a construction is employed in which a shading film called a black mask or a black matrix is formed in a net form around an opening area opposing each pixel on an opposite substrate in order to separate each of the adjacent pixels, preventing mixing of colors between the pixels when a color display using color filters is produced, and further, the contrast ratio is increased regardless of a color display and a black-and-white display.
FIGS. 20 and 21 respectively show an enlarged sectional view and an enlarged plan view of the opposite substrate within a screen display area where a shading film which separates each pixel is formed in this manner and color filters of RGB are formed in each pixel. In FIG. 20, RGB color filters 501 are formed on the surface of an opposite substrate 500 on a side facing the liquid crystal in such a way that the RGB color filters 501 correspond to each pixel. A shading film 502 made of a shading metal or a shading organic film is formed in the spacing of the opening area of each pixel, that is, in the boundary of the color filters 501. Further, a transparent electrode 504 is formed on the color filters 501 via an overcoat (OC) layer 503, which transparent electrode 504 forms a data line or scanning line (in the case of a liquid-crystal panel of a TFD active-matrix driving method, a simple-matrix driving method, or the like), an opposite electrode (in the case of a liquid-crystal panel of a TFT active-matrix driving method), and the like.
As its planar layout, there are the mosaic arrangement, the delta arrangement, and the stripe arrangement, as shown in FIGS. 21A, 21B, and 21C, respectively. In FIGS. 21A, 21B, and 21C, shading film 502a, 502b, and 502c are formed in the boundary areas (that is, the hatched areas in the figures) of the color filters 501a, 501b, and 501c, respectively.
In this type of transmissive-type liquid-crystal panel, the shading films which separate each pixel in this manner makes it possible to generally obtain a very high contrast ratio of, for example, about 100:1. Here, the xe2x80x9ccontrast ratioxe2x80x9d refers to the ratio of the display luminance when a driving voltage is not applied to a liquid crystal, to the display luminance when a driving voltage is applied in the normally white mode, or in the normally black mode.
On the other hand, in a conventional reflective-type liquid-crystal panel using a TN liquid-crystal or a STN liquid-crystal, since the brightness of a display depends on the intensity of external light, generally, a display which is as approximately bright as the brightness in the case of a transmissive-type display cannot be obtained. That is, in a reflective-type liquid-crystal device, insufficient brightness is considered to be more problematical than an insufficient contrast ratio. For this reason, it is a common practice that a shading film is not formed on an opposite substrate like in the case of the above-mentioned transmissive-type liquid-crystal panel.
FIGS. 22 and 23 respectively show an enlarged sectional view and an enlarged plan view of an opposite substrate within a screen display area where a shading film is not formed in this manner and RGB color filters are formed in each pixel. Components which are the same as those in FIGS. 20 and 21 are given the same reference numerals, and accordingly, descriptions thereof have been omitted.
In the reflective-type liquid-crystal panel, since a shading film which separates each pixel in this manner is not formed, the amount of light which passes through the opposite substrate is increased by an amount corresponding to that in which light is not shielded by the shading film, causing the display to be bright. However, because there is no shading film, mixing of colors occurs when a color display using color filters is made. Also, since leakage of light (loss of white) occurs in the spacing (non-opening area) between opening areas for adjacent pixels regardless of color display and black-and-white display, a contrast ratio of, for example, about 10:1 is obtained.
In the manner as described above, in the case of a reflective-type liquid-crystal panel which produces a display using external light, in a dark environment, the display darkens and becomes difficult to see with a decrease in the amount of light. In contrast, in the case of a transmissive-type liquid-crystal panel, such as the above mentioned, which produces a display using a light source such as a backlight, power consumption is increased by an amount corresponding to the light source regardless of whether it is a bright environment or a dark environment, and the transmissive-type liquid-crystal panel is not suitable, in particular, for a portable display device which is operated by a battery.
Therefore, in recent years, a transflective liquid-crystal panel which can be used for both a reflective-type and a transmissive-type has been developed. This transflective liquid-crystal panel produces, mainly in a bright environment, a reflective-type display by controlling the amount of light which is output from the display screen for each pixel by using an optical element, such as a liquid crystal, a polarized-light separator, and so on, disposed on the light path while external light which enters from the display screen is reflected by a transflective film provided inside the device, whereas, mainly in a dark environment, a transmissive-type display is produced by controlling the amount of light which is output from the display screen for each pixel by using an optical element, such as a liquid crystal, a polarized-light separator, and so on, described above, while light-source light is emitted by a built-in light source, such as a backlight, from the rear side of the transflective film.
A liquid-crystal panel driving device for driving various types of liquid-crystal panels, such as a reflective-type, a transmissive-type, or a transflective-type, constructed in the above manner generally comprises driver circuits, such as data-line driving circuits, and scanning-line driving circuits, which supply a data signal and a scanning signal to a plurality of data lines and a plurality of scanning lines, disposed on a substrate on which liquid-crystal elements are formed, respectively, in such a manner as to correspond to display data. This driver circuit is formed on a substrate on which liquid-crystal elements are formed, or provided externally to the liquidcrystal panel. Also, such a liquid-crystal panel driving device comprises a driver control circuit for controlling the driver circuit by supplying, to the driver circuit, (i) various control signals for controlling a voltage value and a supply timing in a data signal and a scanning signal, and (ii) a data signal of a predetermined format, which corresponds to display data and which is based on display data, and the like. Such a liquid-crystal panel driving device further comprises a control power supply circuit for supplying various control potentials, such as a predetermined high potential, low potential, or reference potential, to the driver circuit. The driver control circuit and the control power supply circuit are generally formed as IC circuits and are provided externally to the liquid-crystal panel.
In particular, when the display data is gray scale data, for example, a voltage value (crest value) and an applied time (pulse width) of a data signal are varied in response to each gray scale level by the driver control circuit and driver circuit described above so that the effective value of the applied voltage applied to the liquid crystal is varied in response to the gray scale level. In this case, the setting (that is, the relationship between the gray scale level and the effective value of the applied voltage, or the varying characteristics of the effective value of the applied voltage with respect to the gray scale level) of each magnitude of the effective value of the applied voltage with respect to each gray scale level in the driver circuit, is set to a single setting in advance according to the characteristics of each liquid-crystal panel irrespective of the reflective-type, the transmissive-type, and the transflective-type.
However, in the conventional transflective liquid-crystal panel, similarly to the case of the above-mentioned reflective-type liquid-crystal panel, a construction (see FIGS. 22 and 23) is generally employed in which a shading film which separates each pixel is not provided on an opposite substrate. With such a construction, when a reflective-type display is produced, a display having a contrast ratio of about 10:1 is obtained similarly to the case of the reflective-type liquid-crystal panel. However, when a transmissive-type display is produced, since light-source light exits from the spacing of pixels with no shading film (non-opening area), only a contrast ratio much lower than the above contrast ratio can be obtained. For this reason, in the conventional transflectivetype liquid-crystal panel, there is a problem in that a satisfactory contrast ratio cannot be obtained during the transmissive-type display time. Furthermore, when the display mode is switched from the reflective-type display mode to the transmissive-type display mode, the contrast ratio is decreased greatly at the instant of switching. Alternatively, when the display mode is conversely switched from the transmissive-type display mode to the reflective-type display mode, the contrast ratio is increased greatly at the instant of switching. For this reason, there is also a problem in that incongruity of vision is given to a user at the time of switching of the display mode.
If, for the transflective liquid-crystal panel, a construction (FIGS. 20 and 21) is employed in which a shading film which separates each pixel is provided on an opposite substrate in a manner similar to the above-mentioned transmissive-type liquid-crystal panel, a satisfactory contrast ratio is obtained at the transmissive-type display time. However, since the display darkens at the time of the reflective-type display which depends on the intensity of external light, such a liquid-crystal panel is not used in practice.
As described above, in the liquid-crystal panel driving device, the setting of each magnitude of the effective value of an applied voltage for each gray scale level in the driver circuit is set to a single setting in advance according to the characteristics of each liquid-crystal panel irrespective of whether it is the reflective-type, transmissive-type, or transflective-type. Consequently, by adjusting this setting, it is possible for the transflective-type liquid-crystal panel to respond to the demand for increasing the brightness during a reflective-type display time, such as the brightness described above. It is also possible to respond to the demand for increasing the contrast ratio during the transmissive-type display time. However, there is a problem in that a single setting which satisfies these two demands simultaneously is not available in practice even in a construction in which a shading film is not provided on an opposite substrate.
It is one aspect of the present invention, which has been achieved in view of the above-described problems, to provide a liquid-crystal panel driving device capable of increasing the contrast ratio during a transmissive-type display time while appropriately maintaining the brightness during a reflective-type display time in a transflective-type liquid-crystal panel, and further, which is capable of decreasing the difference between the contrast ratio during the reflective-type display time and the contrast ratio during the transmissive-type display time, and a liquid-crystal device comprising such a liquid-crystal panel and such a driving device.
Therefore, the present invention provides a liquid-crystal panel driving device for driving a transflective-type liquid-crystal panel having a liquid-crystal element which has a liquid crystal held between a pair of substrates and in which the origination state of the liquid crystal can be varied according to the effective value of an applied voltage applied to the liquid crystal; a pair of polarized-light separation devices disposed with the liquid-crystal element interposed therebetween; and a light source for causing light-source light to enter the liquid-crystal element via the polarized-light separation devices, a reflective-type display is produced by causing external light to be reflected via the liquid-crystal element and the polarized-light separation devices when the light source is not switched on, and a transmissive-type display is produced by causing the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation devices when the light source is switched on, the liquid crystal panel driving device comprising: a power supply device for supplying to the liquid-crystal element the applied voltage having an effective value of a magnitude corresponding to the gray scale level indicated by gray scale data; and a switch for switching the setting of each magnitude of the effective value for each gray scale level in the power supply device to a setting for a reflectivetype display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source.
According to the liquid-crystal panel driving device of the present invention, the power supply device supplies an applied voltage having an effective value corresponding to a gray scale level indicated by gray scale data to a liquid-crystal element. Therefore, when the light source is not switched on, if the alignment state of the liquid crystal of the liquid-crystal element varies in accordance with the effective value of this applied voltage, the transmittance with respect to the external light reflected via the liquid-crystal element and the polarized-light separation device varies according to the alignment state. For this reason, the reflected light of the external light, attenuated in response to the gray scale level, is output from the display screen, that is, a reflective-type display is produced. In addition, when the light source is switched on, if the alignment state of the liquid crystal of the liquid-crystal element varies in accordance with the effective value of this applied voltage, the transmittance with respect to the light-source light to be transmitted through the liquid-crystal element and the polarized-light separation device varies according to the alignment state. For this reason, the light-source light attenuated in response to the gray scale level is output from the display screen, that is, a transmissive-type display is produced. Here, in particular, the switch switches the setting of each magnitude of the effective value of the applied voltage for each gray scale level in the power supply device to a setting for a reflective-type display in response to the non-switching on of the light source or to a setting for a transmissive-type display in response to the switching on of the light source.
Therefore, in comparison with a setting (a single setting) in which there is no distinction between that for a reflective-type display and that for a transmissive-type display as in the conventional case, if the setting for the reflective-type display is such a setting as to make the brightness bright and the setting for the transmissive-type display is such a setting as to increase the contrast ratio, a reflective-type display which is brighter than in the conventional case can be produced when the light source is not switched on, and at the same time, when the light source is switched on, a transmissive-type display can be produced at a contrast ratio higher than in the conventional case. In particular, for the trade-off of slightly decreasing the contrast ratio, the setting for the reflective-type display can be made such as to make the brightness correspondingly bright, and at the same time, for the trade-off of slightly reducing the brightness, the setting for the transmissive-type display can be made such as to increase the contrast ratio correspondingly.
In addition, when there is no shading film in the liquid-crystal element (see FIGS. 22 and 23), if the setting for the reflective-type display and the setting for the transmissive-type display are performed so that, by increasing the contrast ratio during the transmissive-type display time or by decreasing the contrast ratio during the reflective-type display time, the difference between the contrast ratio during the reflective-type display time and the contrast ratio during the transmissive-type display time is decreased to that in the conventional case and, preferably, is of the same degree, the variation of the contrast ratio when the light source is switched on or when it is not switched on can be decreased to such a degree so as not to be very conspicuous or noticeable.
As a result of the above, the brightness and the contrast ratio are appropriately adjusted by the liquid-crystal panel driving device of the present invention in both the reflective-type display mode and the transmissive-type display mode, and further, the variations of the contrast ratio and the brightness when these display modes are switched are not visually conspicuous, and a congruous display which is very easy to see can be realized by the transflective-type liquid-crystal panel.
The xe2x80x9cmagnitude of the effective value of the applied voltagexe2x80x9d may be, for example, a voltage value itself of an applied voltage, such as a crest value when a pulse-shaped voltage signal having a predetermined pulse width is applied, or may be a voltage applied time such as a pulse width when a pulse-shaped voltage signal having a predetermined crest value is applied, or may be a two-dimensional applied-voltage density in a screen display area, such as a ratio of the number of pixels, to which a voltage for the total number of pixels in a very small block formed of a plurality of pixels, is applied. That is, when any publicly known gray scale display method is employed, in the transflective-type liquid-crystal panel, the present invention functions effectively, and the above-described operations and effects which are characteristic of the present invention can be obtained.
In one aspect of the liquid-crystal panel driving device of the present invention, the liquid-crystal element further comprises a plurality of data lines, disposed on the substrate, to which a data signal is supplied, and a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data line and the scanning line, respectively. The power supply device comprises a data-signal supply device for supplying to the data line the data signal having a pulse width corresponding to the gray scale level. The switch switches the setting of each pulse width of the data signal with respect to each gray scale level in the data-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source, thereby switching the setting of each magnitude of the effective value.
According to this aspect, the data-signal supply device supplies to the data line a data signal having a pulse width corresponding to the gray scale level. Thereupon, an applied voltage is applied to the liquid crystal of the liquid-crystal element for each liquid crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal supplied via the data line and the scanning line, respectively. Here, in particular, when the switch switches the setting of each pulse width of the data line with respect to each gray scale level in the data-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source or to a setting for a transmissive-type display in response to the switching on of the light source, the setting of each magnitude of the effective value of the applied voltage is switched to a setting for a reflective-type display or to a setting for a transmissive-type display. Therefore, by using the period of the data signal obtained by pulse-width-modulating (PWM) gray scale data, a bright reflective-type display can be produced when the light source is not switched on, and when the light source is switched on, a transmissive-type display can be produced at a high contrast ratio. Further, the variation of the contrast ratio when the light source is switched on or when it is switched off can be decreased to such a degree so as not to be very conspicuous or noticeable.
In this aspect, the switch may comprise a first pulse generator for generating a first pulse signal for gray scale control, formed of a plurality of pulses arranged in correspondence with the intervals of the gray scale level which is a reference for the setting of the pulse width for the reflective-type display; second pulse generator for generating a second pulse signal for gray scale control, formed of a plurality of pulses arranged in correspondence with the intervals of the gray scale level which is a reference for the setting of the pulse width for the transmissive-type display; and a pulse signal switch for selectively supplying the first pulse signal for gray scale control to the data-signal supply device in response to the non-switching on of the light source and for selectively supplying the second pulse signal for gray scale control to the data-signal supply device in response to the switching on of the light source.
With such a construction, the first pulse signal for gray scale control is generated by the first pulse generator, whereas the second pulse signal for gray scale control is generated by the second pulse generator. Then, in response to the non-switching on of the light source, the first pulse signal for gray scale control is selectively supplied to the data-signal supply device by the pulse signal switch. Alternatively, in response to the switching on of the light source, the second pulse signal for gray scale control is selectively supplied to the data-signal supply device by the pulse signal switch. Therefore, a relatively simple switching operation by the pulse signal switch makes it possible to quickly and reliably switch between the reflective-type display mode and the transmissive-type display mode.
In another aspect of the liquid-crystal panel driving device of the present invention, the liquid-crystal element further comprises a plurality of data lines, disposed on the substrate, to which a data signal is supplied, a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied, the applied voltage being applied to the liquid crystal for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied through the data line and the scanning line, respectively. The power supply device comprises data-signal supply device for supplying to the data line the data signal having a pulse width corresponding to the gray scale level, and scanning-signal supply device for supplying to the scanning line the scanning signal having a predetermined width. The switch switches the setting of a crest value of the scanning signal in the scanning-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source and to a setting for a transmissive-type display in response to the switching on of the light source, thereby switching the setting of each magnitude of the effective value.
According to this aspect, the data-signal supply device supplies a data signal having a pulse width corresponding to the gray scale level to the data line. At the same time, the scanning-signal supply device supplies a scanning signal having a predetermined width to the scanning line. Thereupon, an applied voltage is applied to the liquid crystal of the liquid-crystal element for each liquid-crystal portion in each pixel in such a manner as to correspond to at least one of the data signal and the scanning signal which are supplied via the data lines and the scanning lines, respectively. Here, in particular, when the switch switches the setting of the crest value of the scanning signal in the scanning-signal supply device to a setting for a reflective-type display in response to the non-switching on of the light source or to a setting for a transmissive-type display in response to the switching on of the light source, the setting of each magnitude of the effective value of the applied voltage is switched to a setting for a reflective-type display or to a setting for a transmissive-type display. Therefore, by using the magnitude of the voltage value of the applied voltage based on the difference between the data-signal voltage and the scanning-signal voltage, a bright reflective-type display can be produced when the light source is not switched on, and when the light source is switched on, a transmissive-type display can be produced at a high contrast ratio. Further, the variation of the contrast ratio when the light source is switched on and when it is switched off can be decreased to such a degree so as not to be very conspicuous or noticeable.
In this aspect, the switch may comprise a first control voltage supply for supplying a first control voltage which is a reference for the setting of the crest value for the reflective-type display; a second control voltage supply for supplying a second control voltage which is a reference for the setting of the crest value for the transmissive-type display; and a control voltage switch for selectively supplying the first control voltage to the scanning-signal supply device in response to the non-switching on of the light source and for selectively supplying the second control voltage to the scanning-signal supply device in response to the switching on of the light source.
With such a construction, the first control voltage supply supplies a first control voltage, whereas the second control voltage supply supplies a second control voltage. Then, in response to the non-switching on of the light source, the control voltage switch selectively supplies the first control voltage to the scanning-signal supply device. Alternatively, in response to the switching on of the light source, the control voltage switch selectively supplies the second control voltage to the scanningsignal supply device. Therefore, a relatively simple switching operation by the control voltage switch makes it possible to quickly and reliably switch between the reflective-type display mode and the transmissive-type display mode.
In another aspect of the liquid-crystal panel driving device of the present invention, the switch switches the setting of the magnitude of the effective value in such a way that in the setting for the reflective-type display, the transmittance of the external light in the liquid-crystal device becomes relatively large over the entire region of the gray scale level, and that in the setting for the transmissive-type display, the transmittance of the light-source light in the liquid-crystal device becomes relatively small over the entire region of the gray scale level.
According to this aspect, since, in the reflective-type display mode, the transmittance of the external light in the liquid-crystal device becomes relatively large over the entire region of the gray scale level by switching using the switch, the display becomes bright over the entire gray scale. Conversely, in the transmissive-type display mode, since the transmittance of the light-source light in the liquid-crystal device becomes relatively small over the entire region of the gray scale level by switching using the switch, the display becomes dark over the entire gray scale. Therefore, when, in particular, there is no shading film in the liquid-crystal element (see FIGS. 22 and 23), the difference in the contrast ratio and in the brightness between during the reflective-type display time and during the transmissive-type display time can be reduced as well, and the variation of the contrast ratio and the brightness when the light source is switched on or when it is switched off can be decreased to such a degree so as not to be very conspicuous or noticeable.
In another aspect of the liquid-crystal panel driving device of the present invention, the switch switches the setting of the magnitude of the effective value in such a way that, in the setting for the reflective-type display, the variation of the transmittance of the external light in the liquid-crystal device with respect to the variation of the gray scale level becomes relatively small, and that in the setting for the transmissive-type display, the variation of the light-source light in the liquidcrystal device with respect to the variation of the gray scale level becomes relatively large.
According to this aspect, since the switching by the switch causes the variation of the transmittance of the external light with respect to the variation of the gray scale level to become relatively small in the reflective-type display mode, the contrast ratio becomes small. In contrast, in the transmissive-type display mode, since the variation of the transmittance of the external light with respect to the variation of the gray scale level becomes relatively large, the contrast ratio becomes large. Therefore, when, in particular, there is no shading film in the liquid-crystal element (see FIGS. 22 and 23), the difference in the contrast ratio between during the reflective-type display time and during the transmissive-type display time can be reduced as well, and the variation of the contrast ratio when the light source is switched on or when it is switched off can be decreased to such a degree so as not to be very conspicuous or noticeable.
In another aspect of the liquid-crystal panel driving device of the present invention, there is further provided a switching-on control device for controlling the switching-on and the non-switching-on of the light source. The switch switches the setting of the magnitude of the effective value in synchronization with the control of the switching-on and the non-switching-on by the switching-on control device.
According to this aspect, the switching-on control device controls the switching-on and the non-switching-on of the light source. Thereupon, the switch switches the setting of the magnitude of the applied voltage in synchronization with the control of the switching-on and the non-switching-on by the switching-on control device. Therefore, in response to the non-switching-on (switching off) and the switching-on of the light source, it is possible to switch between the setting for the reflective-type display and the setting for the transmissive-type display reliably and without delay.
In order to achieve the above objects, the liquid-crystal device of the present invention comprises the above-described liquid-crystal panel driving device according to the present invention and a liquid-crystal panel.
According to the liquid-crystal device of the present invention, since the liquid-crystal device comprises the above-described driving device of the present invention, it is possible to produce a display at an appropriately adjusted brightness and at a contrast ratio in both the reflective-type display mode and the transmissive-type display mode. Furthermore, the variation of the contrast ratio and the brightness when these display modes are switched is not visually conspicuous, and a congruous display which is very easy to see can be produced.
According to one aspect of the liquid-crystal device of the present invention, the liquid-crystal element comprises a plurality of data lines, disposed on a substrate, to which a data signal is supplied; a plurality of scanning lines, disposed on the substrate, to which a scanning signal is supplied; and a plurality of two-terminal-type non-linear elements which are connected in series, respectively, together with the liquid-crystal portion in each pixel between the plurality of data lines and the plurality of scanning lines.
According to this aspect, a data signal is supplied from the data line to the liquid-crystal portion in each pixel via the two-terminal-type non-linear element connected in series with the liquid-crystal portion, and a scanning signal is supplied thereto from the scanning line. Therefore, for example, by using the magnitude of the voltage value of an applied voltage based on the difference between the data-signal voltage and the scanning-signal voltage and the period of the pulse width of the data signal, a bright reflective-type display can be produced when the light source is not switched on, and when the light source is switched on, a transmissive-type display can be produced at a high contrast ratio.
In this aspect, the two-terminal-type non-linear element may comprise a TFD (Thin Film Diode) driving element.
With such a construction, in a transflective liquid-crystal panel for use with a TFD active-matrix driving method, a bright reflective-type display can be produced when the light source is not switched on, and when the light source is switched on, a transmissive-type display can be produced at a high contrast ratio.
As an applicable transflective liquid-crystal panel of the present invention, in addition to a liquid-crystal panel for use with a TFD active-matrix driving method, there are various liquid-crystal panels, such as a liquid-crystal panel for use with a TFT active-matrix driving method, or a liquid-crystal panel for use with a simple-matrix driving method. That is, when any publicly known liquid-crystal panel is employed, in the transflective liquid-crystal panel, the present invention functions effectively, and the above-described operations and effects which are characteristics of the present invention can be obtained.
In another aspect of the liquid-crystal device of the present invention, a pair of polarized-light separation devices comprise a pair of polarizers disposed in such a way that their transmission axes form a predetermined angle, the liquid-crystal panel further comprises a transflector disposed on a side opposite to the liquid-crystal element with respect to one of the pair of polarizers, and the light source causes the light-source light to enter the liquid-crystal element via the transflective film and the one polarizer.
According to this aspect, when the light source is not switched on, the external light enters the liquid-crystal element via the other (the polarizer of the display screen side) of the pair of polarizers disposed in such a way that their transmission axes form a predetermined angle (for example, 90 degrees when a TN liquid-crystal element is provided and a normally white mode is set, 0 degree when a TN liquid-crystal element is provided and a normally black mode is set, and the like), and the external light is further reflected by a transflective film via the one polarizer (the polarizer in an inner part close to the light source). Thereafter, the reflected external light is selectively output from the display screen via one polarizer, the liquid-crystal element, and the other polarizer according to the alignment state of the liquid-crystal element. Therefore, when the light source is not switched on, a reflective-type display is produced. Also, when the light source is switched on, the light-source light enters the liquid-crystal element via the transflective film and one of the polarizers, and is further selectively output from the display screen via the other polarizer according to the alignment state of the liquid-crystal element. Therefore, when the light source is switched on, a transmissive-type display is produced.
One or both of the pair of the polarized-light separation devices may be formed of a publicly known polarized-light separator, such as a reflection polarizer, other than a polarizer, such as polarization plate. For example, if the polarized-light separation device is formed of a reflection polarizer, since polarized-light separation is performed by reflection, efficiency of use of light is higher than a case in which a polarizer is used, and the brightness at a reflective-type display is increased correspondingly. Furthermore, the construction may be formed in such a way that a reflection polarizer disposed on a region close to the light source is made to have the function of a transflective film. Furthermore, there is a case in which so-called positive-negative inversion occurs between a reflective-type display and a transmissive-type display depending upon the properties and combination of polarized-light separation devices to be employed. When positive-negative inversion opposite measure technology is performed on this inversion, the present invention functions effectively as well.
The above operations and other advantages of the present invention will become apparent from the embodiments described below.